In a liquid crystal display device, or the like, the display panel and the driving circuits (drivers) for driving the display panel are typically connected to each other using a conventional TCP (Tape Carrier Package)-based structure.
FIG. 1 is a diagram schematically illustrating the structure of a liquid crystal module using the conventional TCP-based structure. In the module structure of FIG. 1, a plurality of gate TCPs 12 and a plurality of source TCPs 14 are connected to a gate terminal region and a source terminal region, respectively, of a display panel 11 via an anisotropic conductive film (hereinafter referred to as “ACF”). A gate PWB (Printed Wire Board) 13 and a source PWB 15 are connected to the gate TCPs 12 and the source TCPs 14, respectively, via ACF. The gate PWB 13 and the source PWB 15 are each connected to an FPC 16, which is connected to an external circuit board.
Although this TCP-based module structure has long been used in mass production, it requires a large number of components, and the material cost and the assembly cost are high. In view of this, a PWB-free structure as illustrated in FIG. 2 has been researched in the art.
A PWB-free module structure does not include PWBs as described above. In the PWB-free structure illustrated in FIG. 2, a plurality of gate TCPs 22 and a plurality of source TCPs 23 are connected to a gate terminal region and a source terminal region, respectively, of a display panel 21, and an FPC 24 is connected to the source terminal region. The FPC 24 is connected to an external circuit board, from which a gate driving power supply/signal and a source driving power supply/signal are supplied.
The gate driving power supply/signal received through the FPC 24 is transmitted successively through the gate TCPs 22 via a panel line 27 provided on the display panel 21. Similarly, the source driving power supply/signal received through the FPC 24 is transmitted successively through the source TCPs 23 via the panel line 27 provided on the display panel 21.
Next, a conventional PWB-free connection structure will be described with reference to FIG. 4 and FIG. 5. In the following description, the direction in which a plurality of TCPs are arranged in the source terminal region of the display panel 21 will be referred to as the “x direction”, and a direction which crosses (typically substantially perpendicular to) the x direction will be referred to as the “y direction”. Moreover, referring to FIG. 3, a direction 4 that is perpendicular to a side surface 3 of a substrate 2 including an edge of the substrate 2 along which a terminal 1 at one end of a line 6 is located will be referred to herein as the “terminal termination direction”. Where a plurality of terminals 1 are provided, a direction 5 in which the terminals 1 are arranged will be referred to as the “terminal arrangement direction”.
FIG. 4 is an enlarged view of a broken line section in FIG. 2, illustrating a portion of a liquid crystal module structure disclosed in Japanese Laid-Open Patent Publication No. 7-049657 (FIG. 3). As illustrated in FIG. 4, a driving circuit 35 is mounted on each TCP 23, and the driving circuit 35 includes input terminals 54 and output terminals 55. The TCP 23 further includes first terminals 31, second terminals 32, third terminals 33 and TCP lines 34. The TCP lines 34 are connected to the first terminals 31 and the third terminals 33.
In the TCP 23, the source driving power supply/signal is supplied from the first terminals 31 to the lines 34 and output from the third terminals 33. The source driving power supply/signal output from the third terminals 33 is input to the first terminals 31 of the next TCP 23 via panel lines 27a and panel terminals 27b, which are formed on the display panel. Thus, adjacent TCPs 23 are electrically connected to each other via the panel lines 27a and the panel terminals 27b, which are formed on the display panel.
The source driving power supply/signal supplied to the lines 34 is input to the driving circuit 35 via the input terminals 54. The signal is output from the driving circuit 35 through the output terminals 55 and is supplied to other lines (not shown) on the display panel such as source lines or gate lines via the second terminals 32 of the TCP 23.
Next, the first terminals 31 and the third terminals 33 will be described in greater detail.
As described above, adjacent TCPs 23 are electrically connected to each other via the panel lines 27a and the panel terminals 27b, which are formed on the display panel. The panel lines 27a and the panel terminals 27b electrically connect the first terminals 31 of the TCP 23 with the third terminals 33.
As illustrated in FIG. 4, some terminals 31a among the plurality of the first terminals 31 are arranged in the y direction, and the terminal termination direction thereof is the −x direction. Similarly, some terminals 33a among the plurality of third terminals 33 are arranged in the y direction, and the terminal termination direction thereof is the x direction. The terminals 31a and the terminals 33a are facing each other with a small interval therebetween, and therefore are connected to each other via the panel terminals 27b formed on the display panel. The other terminals 31b of the first terminals 31 and the other terminals 33b of the third terminals 33 are arranged in the x direction, and the terminal termination direction thereof is the y direction. The terminals 31b and the terminals 33b are not facing each other and the interval therebetween is much larger than that between the terminals 31a and the terminals 33a. Therefore, the terminals 31b and the terminals 33b are connected to each other via the panel lines 27a, which are routed on the display panel 21. As can be seen in FIG. 4, the panel lines 27a are much longer than the panel terminals 27b because of the terminals 31b and the terminals 33b not facing each other.
In the connection structure illustrated in FIG. 4, the terminals 31a and 33a of the first terminals 31 and the third terminals 33 are arranged in the y direction and the terminal termination direction thereof is the −x or x direction. Therefore, the width (dimension in the y direction) of the terminal region can be made smaller than that in a case where all of the first terminals 31 and the third terminals 33 are arranged in the x direction so that the termination direction thereof is the y direction, as are the terminals 31b and 33b. 
FIG. 5 is a diagram illustrating TCPs disclosed in Japanese Laid-Open Patent Publication No. 06-3684 (FIG. 4). A driving circuit 44 is mounted on each TCP 41. The TCP 41 includes TCP lines 42, and the lines 42 are connected to the driver IC 44. As illustrated in FIG. 5, a plurality of TCPs 41 arranged adjacent to one another in the x direction are attached to an edge of the display panel (not shown in FIG. 4) extending in the x direction. The TCP lines 42 extending in the x direction and formed in the adjacent TCPs 41 are connected to each other with their connected portions 43 being soldered together.
With the PWB-free structure described above with reference to FIG. 4 and FIG. 5, as compared to the TCP-based structure, the number of components can be reduced significantly, thereby also reducing the material cost and the assembly cost. However, the PWB-free structure has the following problems.
With the line structure of FIG. 4, the terminals 31a and 33a among the first and third terminals formed in the TCP are arranged in the y direction and the termination direction thereof is the x or −x direction, whereas the other terminals 31b and 33b are arranged in the x direction and the termination direction thereof is the y or −y direction. While the number of connection terminals required is usually about 30 to 60, the maximum number of terminals that can be arranged in the y direction, as with the terminals 31a and 33a, is about 5 (when the length of a connection terminal is 1 mm). Therefore, the rest of the terminals are all arranged in the x direction, as with the terminals 31b and 33b. As described above, the terminals 31b and the terminals 33b, which are arranged in the x direction, are connected to each other via the much longer panel lines 27a formed on the display panel.
However, the conductive film formed on the display panel has a thickness of less than 1 μm, typically some hundreds of nanometer, and thus has a high sheet resistance. Thus, lines formed by using the conductive film on the panel have a high sheet resistance. Therefore, when the terminals 31b and the terminals 33b are connected to each other by using the much longer panel lines 27a, which are routed on the display panel, the connection resistance is very high, thereby deteriorating the signal being supplied to the driving circuit of a TCP. Then, the driving circuit may not operate normally. Particularly, a source driving circuit of a liquid crystal panel is sensitive to signal deterioration. Therefore, no liquid crystal modules having source driving circuits which are attached to the panel using a PWB-free structure have been commercially manufactured and sold in the market.
In the structure illustrated in FIG. 5, the lines 42 formed in the adjacent TCPs 41 are directly connected to each other via the connected portions 43. Therefore, it is not necessary to route the panel lines on the display panel to connect the lines 42 formed in the adjacent TCPs 41 to each other. Thus, the structure of FIG. 5 does not suffer from the increase in the resistance value as does the connection structure of FIG. 4. However, the lines 42 formed in the adjacent TCPs 41 are soldered to each other, and the connection step needs to be performed completely separately from the step of positioning and fixing the TCPs on the display panel. This increases the production steps and the cost therefor. Moreover, it is difficult to realize a minute pitch with soldering as compared with ACF connection. For example, for the connection of 60 lines with a pitch of 0.3 mm, a connection area as long as 18 mm is required. Therefore, the size of the terminal region on the display panel increases, and the TCP area increases, thereby increasing the cost.